First of all, PLEASE do not kill yourself. I know that you're in great pain but that is the flip side of caring for someone.
Most relationships go through a six- to eight-month "honeymoon phase" where everything is better than best. Then the shine wears thin and reality kicks in. The "cute" habits that one had now become annoying to the other. This can be the hardest time in a relationship--the person you thought you knew has suddenly been kidnapped by aliens and replaced by a horrible, uncaring, thoughtless person.
This is the time where give and take is especially important and if both won't try then there's no relationship. One can't try for the both (I speak from experience). Based on what you say there was a big hiccup in your relationship and it ended. Period.
Yes, it sounds like you made a mistake and want to make things better. It is also possible that the other person just isn't interested in anything but the "honeymoon" phase of the relationship. Falling in love can blind one to the reality of the situation. It's possible there were clues in that time that you may have missed because you were elsewhere occupied. If this guy left "just because" and has taken up with someone else then he's not the person he portrayed himself to be (or you thought he was).
It's a cruel thing to say but you're probably better off without him and it's time to move on. You've learned a hard lesson but it will stay with you for the rest of your life. Not that you won't make the same mistake (I'm 50 and have made it several times) but maybe it won't happen every time.
What do you do? Start a new life. Find new friends, new interests. Stay away from mutual friends that might tell you (mistakenly out of friendship) what he is doing. You DON'T CARE what he is doing. Remove his phone number from every place you have it and NO TEXTING. Stay away from him.
It will take awhile to get over this, but you will. Go ahead and mourn your loss but, if you have to, get out and be among people. Force yourself to go to the mall just to walk around and get away from where you live and all the gloom. Keep a journal where you can pour your heart out--I have several of those. If you have a support network (friends, family) now is the time to use it. You don't have to go through this alone.
Good luck and please keep posting.
